Communication speeds in data communication lines have increased dramatically in recent years. Accordingly, transmission/reception of large-capacity visual information including moving-picture image data and audio data is now regularly performed even among information terminals such as individually-owned personal computers (hereinafter referred to as PCs) and the like. Particularly, in such a communication environment, a system that realizes real-time bidirectional data communication can be easily built. The area (a) in FIG. 1 is a view showing a configuration of a bidirectional data communication system such as a video teleconference system that can be built utilizing existing network resources including a network line and an information terminal such as a PC. The bidirectional data communication system comprises a network 100, and a plurality of information terminals (terminal A 110, terminal B 120, and terminal C 130) individually connected to the network 100. In addition, transmission/reception 100a (including transmission requirement and data distribution) of visual information such as moving-picture image data is performed via the network 100 between the terminal A 110 and the terminal B 120 which constitute a part of the system. In a similar manner, transmission/reception 100b of visual information such as moving-picture image data is performed via the network 100 between the terminal A 110 and the terminal C 130. Transmission/reception 100c (including transmission requirement and data distribution) of visual information such as moving-picture image data is performed via the network 100 between the terminal B 120 and the terminal C 130. Moreover, the terminal A 110 comprises a control unit 110a (which corresponds to a CPU in a PC), the terminal B 120 comprises a control unit 120a, and the terminal C 130 comprises a control unit 130a. Actual communication control and various digital processing are performed by the control units 110a to 130a. 
However, under present circumstances, when distributing a vast amount of moving-picture image data using limited network resources, the data amount itself must be reduced due to limitations in processing capacities of the respective information terminals, network line speed, and the like. Therefore, techniques for compressing moving-picture image data and audio data to be distributed are being actively studied and commercialized. For example, Patent Document 1 discloses an image communication technique for enabling image data transmission/reception suited to a communication environment in accordance with a terminal type of a reception-side client or the like without imposing an inordinate burden on an operator or respective information terminals. On the other hand, Patent Document 2 discloses an encoding apparatus that utilizes scalability, a method and a program thereof, and the like as a system that realizes information updatability with respect to a resolution direction.
In addition, Patent Document 3 discloses a technique that enables data communication suited to individual communication environments between a server and a reception-side client. In other words, when a network line speed between the server and the reception-side client is low with respect to quality of image data transmitted from the server, image data whose quality corresponds to a requirement from the reception-side client is transmitted from the server to the reception-side client.